sh: Shut up compiler warnings in __do_page_fault().

GCC doesn't seem to be able to figure this one out for
itself, so just shut it up..

  CC      arch/sh/mm/fault.o
arch/sh/mm/fault.c: In function '__do_page_fault':
arch/sh/mm/fault.c:288: warning: 'ptl' may be used uninitialized in this function
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/mm/fault.c

@@ -285,7 +285,7 @@ asmlinkage int __kprobes __do_page_fault(struct pt_regs *regs,
 	pte_t *pte;
 	pte_t entry;
 	struct mm_struct *mm = current->mm;
-	spinlock_t *ptl;
+	spinlock_t *ptl = NULL;
 	int ret = 1;
 
 #ifdef CONFIG_SH_KGDB